WO2010121977A1

WO2010121977A1 - Magnetic alloy material and process for the production thereof

Info

Publication number: WO2010121977A1
Application number: PCT/EP2010/055086
Authority: WO
Inventors: Julia Lyubina; Oliver Gutfleisch
Original assignee: Leibniz-Institut Für Festkörper- Und Werkstoffforschung Dresden E.V.
Priority date: 2009-04-24
Filing date: 2010-04-19
Publication date: 2010-10-28
Also published as: DE102009002640A1; EP2422347B1; EP2422347A1

Abstract

The invention relates to the field of materials science and materials physics and concerns a magnetic alloy material, which can be used, for example, as a magnetic cooling material (magnetocaloric material) for cooling purposes or for energy generation purposes, and a process for the production thereof. The aim of the present invention is to provide a magnetic alloy material which has comparable magnetic and/or magnetocaloric properties and improved mechanical properties compared to prior art materials. This aim is achieved by a magnetic alloy material which displays a magnetocaloric effect and has a foam-like structure with an open porosity of from 1% to 50% and/or a closed porosity of at least 1% or in which particles of the magnetic alloy material are embedded in a matrix material having a higher ductility than the magnetic alloy material.

Description

Magnetic alloy material and process for its production

The invention relates to the field of materials science and material physics and relates to a magnetic alloying material, which can be used, for example, as a magnetic cooling material (magnetocaloric material) for cooling purposes or for power generation purposes, and a method for its preparation.

Magnetic cooling by magnetic alloy materials provides an environmentally friendly, energy and cost effective alternative to conventional gas compression refrigeration. The magnetic cooling is based on the magnetocaloric effect (MCE = magnetocaloric effect) in which a temperature change occurs due to the change in the magnetization of the material. For applications, especially materials with a large MCE are interesting.

Magnetic materials with a crystal structure of NaZni ₃ type show a particularly large MCE, which is caused by a thermally and field-induced phase transition from the paramagnetic to the ferromagnetic state near the Curie temperature T _{0 of} the material. Magnetic alloy materials of the NaZrH ₃ crystal structure are known and could be used as magnetic cooling materials. The composition of such materials may be represented by the formula R (Ti _-a M _a) i3Hd be given, with rare-earth elements for R, or a combination rare earth elements for T is Fe or a combination of Fe and Co and M Al, Si, Ga, or Ge, or Combinations thereof are used. For a, 0.05 <a <0.2 and for d, 0 <d <J3.0. Such materials have very good magnetocaloric properties at temperatures near Curie temperature and are considered to be promising candidates for magnetic cooling [C. Zimm et al., Int. J. Refrigeration 29, 1302 (2006)].

As is known, such magnetic alloys are produced by means of an arc or high-frequency melting process and then heat-treated for about 168 hours at about 1050 ^° C. under vacuum (DE 103 38 467 A1). It is also possible to melt the alloying elements at 1200 to 1800 ⁰ C, then cool with cooling rates of 10 ² to 10 ⁶ ° C / s (rapidly solidify) and then thermally treat the rapidly solidified alloy [US 2006/0076084 A1; A. Yan, K.-H. Müller, O. Gutfleisch, J. Appl. Phys. 97, 036102 (2005); XB Liu, Z. Altounian, GH Tu, J. Phys .: Condens. Matter 16, 8043 (2004)].

Furthermore, a number of magnetic alloys, such as Gd ₅ Si ₂ Ge ₂ , MnAs, Mni _-x Fe _x As, Ni ₂ MnSn and (Mn ₁ Fe) ₂ (P ₁ As) are known, which show in part a particularly large MCE by causing a thermally and / or field-induced magnetic phase transition near the Curie temperature T ₀ and / or near a structural phase transition [VK Pecharsky and KA Gschneidner, Jr., Phys. Rev. Lett. 78, 4494 (1997); H. Wada and Y. Tanabe, Appl. Phys. Lett. 79, 3302 (2001); A. de Campos et al., Nature Materials 5, 802 (2006); T. Krenke et al., Nature Materials 4, 450 (2005); O. Tegus, E. Bruck, KHJ Buschow, and FR de Boer, Nature 415, 150 (2002); DE 103 38 467 A1, US 2007/0137732 A1, US 2004/007944 A1, US Pat. No. 7,186,303 B2, US 2006/0231163; US Patent 7069729].

A significant disadvantage of these alloys is known to be the occurrence of volume changes due to isotropic or anisotropic expansion of the crystal lattice during the magnetic or structural phase transition, especially for the alloys showing a first-order phase transition [A. Fujita et al., Phys. Rev B 65, 014410 (2001); H. Yabuta et al., J. Phys. Soc. Japan, 75, 113707 (2006)]. These changes in volume can result in significantly reduced mechanical integrity and thus severely limiting conditions of use.

The object of the present invention is to provide a magnetic alloying material which has improved mechanical properties with comparable magnetic and / or magnetocaloric properties over the prior art materials, and an indication of an effective method for producing the magnetic alloy material.

The object is achieved by the invention specified in the claims. Advantageous embodiments are the subject of the dependent claims.

The magnetic alloy material of the present invention which exhibits a magnetocaloric effect and which has a foam-like structure with an open porosity of 1% to 50% and / or a closed porosity of at least 1%, or wherein the particles of the magnetic alloy material in a matrix material with a higher ductility than the magnetic alloy material are embedded.

Advantageously,> 35% by volume of the magnetic alloy material has a NaZni ₃ type crystal structure, more preferably at least 50% by volume, more preferably 80-90% by volume, of the magnetic alloy material having a NaZni ₃ crystal structure Type on.

Also advantageously, the magnetic alloy material has a composition according to the formula:

R _a Fei00-axy-zT _x MyL _z with

R = La or a combination of La with Ce, Pr, Nd, Sm, Gd, Tb,

Dy, Ho, Er, Tm, Yb, Lu and / or Y, T = at least one element selected from the group Sc, Ti, V, Cr,

Mn, Co, Ni, Cu and / or Zn,

M = Al, Si, P, Ga, Ge, In and / or Sn,

L = H, B, C and / or N,

5 <_a <11 and 0 <x <12 and 2 <y <20 and 0 <z <18, (everything in atomic

Further advantageously, for changing the Curie temperature of the magnetic alloy material, the conditions 2 <z <15 at% and / or 3 5_y 1 16 and / or 0.3 <x <9 are realized, wherein with varying proportion z and / or y and / or x the Curie temperature changes between 170 K and 400 K.

And also advantageously, the foam-like structure of the magnetic alloy material has an open porosity of 2 to 50% and / or a closed porosity of 2 to 50%.

It is also advantageous if particles of the magnetic alloy material with a particle size of 10 nm to 1 mm are embedded in a matrix material.

It is also advantageous if the matrix material with a higher ductility than the magnetic alloy material comprises at least one element of Al, Ag, Au, Bi, C, Co, Cu, Fe, Ga, Ni, Pb, Pd, Pt, Sn, Ti , Zn or combinations and / or reaction products thereof.

It is furthermore advantageous if, in addition to the matrix material, a second material comprising at least one element of Al, Ag, Au, Bi, C, Co, Cu, Fe, Ga, Ni, Nb, Pb, Pd, Pt, Sn, Ta, Ti , V, Zn, Zr or combinations and / or reaction products also with the matrix material thereof is present.

And it is also advantageous if the matrix material has at least a 10% higher ductility than the magnetic alloy material.

It is also advantageous if the particles of the magnetic alloy material are in the form of a band, a wire, a plate, a foil or a flake, a needle or in the form of powder particles. In the method for producing a magnetic alloy material of the present invention, the magnetic alloy material is made into a foam-like structure by means of foaming or compaction, or particles of the magnetic alloy material are mixed with a matrix material having higher ductility than the magnetic alloy material and then heated to the extent that the matrix material forms the matrix around the particles of the magnetic alloy material.

Advantageously, the compaction is carried out by hot or cold pressing.

Also, advantageously, the foaming is carried out by applying a suspension with particles of the magnetic alloy material to a foam-like structure and drying, and subsequently burning out or pyrolyzing the foam-like structure.

Further advantageously, particles of the magnetic alloy material and of the matrix material are mixed and processed into a shaped body and subsequently heated to a temperature at which the matrix material at least softens and covers the particles of the magnetic alloy material substantially completely.

Also advantageously, the application temperature is adjusted by applying a vacuum.

With the solution according to the invention, it becomes possible for the first time to specify a magnetic alloy material whose mechanical properties, in particular the strength (integrity), while maintaining the good magnetic properties with respect to the magnetocaloric effect, have been significantly improved.

This is achieved according to the invention in that the magnetic alloy material has a foam-like structure or particles of the magnetic alloy material are embedded in a matrix material which has a higher ductility than the magnetic alloy material. Foam-like structure is to be understood in the context of this invention, a structure consisting of webs that limit foam cells. These foam cells are open. The web material consists essentially of the magnetic alloy material and has an open and / or closed porosity. Furthermore, the foam-like structure may also consist essentially of only magnetic alloy material with open and / or closed pores.

The magnetic alloy material can be processed in the form of particles in a suspension to a shaped body or applied to a foam structure and processed after drying and a temperature increase to the magnetic alloy material. The particles of the magnetic alloy material may be present in the form of a band, a wire, a plate, a Fol ie or a flake, a needle or in the form of powder particles.

In the case that the magnetic alloy material according to the invention is embedded as particles in a matrix material, the particles may also be in the form of a band, a wire, a plate, a foil or a flake, a needle or in the form of powder particles. The particle size can be from a few nanometers to ~ 100 microns.

The particles of the magnetic alloying matehal can then be mixed with particles of the matrix material and processed into a shaped body. Subsequently, the molding is exposed to a temperature increase, wherein at least one such temperature must be achieved that the matrix material forms a matrix around the particles of the magnetic alloy material and substantially completely covers the surface of the particles as possible.

The magnetic alloy material according to the invention exhibits a significantly higher mechanical strength, since the volume changes of the magnetic alloy material can be significantly better absorbed by the phase transition, which is present at a pore or the ductile matrix material, and thus counteract the cracking and possibly even the destruction of the molding and prevent it partially or completely.

The solution according to the invention shows, in particular, improved results in the predominant use of magnetic alloy materials whose crystal structure is of the NaZni ₃ type. These materials are known to have a large magnetocaloric effect and therefore can be used particularly advantageously.

It is also advantageous if the solution according to the invention for magnetic alloy materials is used, which have a composition according to the formula R _x Tioo- _x -Y- _z M _y L _z with the known elements, element combinations and proportions is.

It is particularly advantageous if in particular H, B, C and / or N are present in the alloy material. These elements are known to be incorporated into interstitial sites and in particular have an effect on the Curie temperature T ₀ , which is known to be important for magnetic alloy materials and which is known to determine the temperature of use, as the Curie temperature is increased as the proportion of these elements, and in particular H, increases. Thus, an application temperature for the magnetic alloy material is adjustable within relatively wide limits.

The effect of loading the magnetic alloy material with these elements is further improved by the solution according to the invention, since the increased brittleness of the magnetic alloy material resulting from the interaction is likewise absorbed by the foam-like structure or the matrix material become.

The Curie or application temperature setting can be done for example by applying a vacuum during the temperature increase, which is also in the compaction by means of hot pressing or pressing at moderate temperatures feasible. About the height of the temperature or time, the application temperature can be adjusted. With a specially selected coating method, such as the electrochemical coating or electroless plating coating, hydrogen can be introduced interstitially into the crystal lattice at the same time or substitute elements such as Co, Ni, Cu by diffusion processes Fe and thereby increase the Curie temperature T ₀ . The hydrogen can be formed in a secondary reaction, such as released as a by-product of a cathodic electrode reaction or during the oxidation of the reducing agent. Thus, this effect is also in the solution according to the invention in almost unchanged manner, so that in addition to improved mechanical properties and improved primary properties, such as application temperature and size of the MCE can be achieved with the inventive solution.

This is achieved by compaction, e.g. By hot or cold pressing, or produced by foaming magnetic alloy material according to the invention has open and / or closed pores, with a particularly advantageous even a regular porosity can be adjusted. By this is to be understood according to the invention that the pores are arranged directionally in the material, so that, for example, an effective flow through a (cooling) liquid can be achieved. A high specific surface area of the porous material is also very advantageous for effective heat exchange.

Due to the porosity according to the invention, the magnetic alloy material according to the invention has a density between 50% and 99% of the theoretically achievable density of the magnetic alloy material.

In the case of the use of the matrix material, this may also contain a further material or the further material may be formed by reactions of the matrix material or of another material. This further material can also be deposited on the surface of the particles of the magnetic alloy material.

Very advantageous is the reduction of the magnetic or thermal hysteresis, which can be achieved with the magnetic alloy material according to the invention. For applications the hysteresis should be minimized. Due to the porosity or the ductility of the second phase does not prevent the volume change or expansion and reduces the hysteresis.

The magnetic entropy change remains virtually unchanged, ie the relative cooling power remains high. The adiabatic temperature change ΔT _aC ι decreases slightly. However, a high reproducibility after significantly more work cycles in comparison to a solid material is advantageous.

The invention will be explained in more detail with reference to two embodiments.

example 1

From the elements La, Fe, and Si, a solid material with the composition LaFen, 6Sii, _{4 is} prepared by induction melting and subsequent heat treatment at 1050 ⁰ C for 7 days. The resulting material consists of 97 wt .-% of the NaZni ₃ -type phase and 3 wt .-% of α-Fe.

Subsequently, 2 plates measuring 8 mm × 4 mm × 1 mm are cut out of the solid material for magnetic property inspection.

The solid material with the composition LaFen, 6Sii, ₄ shows at a magnetic field change of 2 Tesla a maximum entropy change ΔS _ma χ of 162 kJ / m ³ K at 194 K. Here, the half-width is 8 K and the relative cooling capacity is 1, 5 MJ / m ³ . The entropy change and the relative cooling power remain unchanged after thermal cycling.

Nevertheless, a decrease in the adiabatic temperature change ΔT _aC ι is observed. In the first thermal cycle, the maximum adiabatic temperature change ΔT _aC ι ^max at a magnetic field change of 1.9 Tesla 7.3 K at 191 K when cooling from room temperature. When heating up 170 K on Room temperature, the maximum adiabatic temperature change decreases with a magnetic field change from 1, 9 Tesla to 5.2 K at 1 94 K. The thermal hysteresis is 3 K and magnetic hysteresis up to 0.7 T.

During the second and third thermal cycle, ΔT _aC ι ^max decreases to 6.7 K and 6.6 K during cooling from room temperature and to 5 K and 4.9 K during heating of 170 K to room temperature. The thermal hysteresis is 2.2 K and 2.1 K in the second and third thermal cycle.

The reduction in adiabatic temperature change and thermal hysteresis is largely due to microscopic cracking that can lead to loss of mechanical integrity after multiple thermal or field cycling cycles.

According to the invention, a porous, foam-like material from the pulverized solid material by hot pressing at press temperature of 600 - 1423 K, and pressing pressure of the order of ~ 10 ² - 10 ³ MPa prepared. The resulting material consists of 91% by weight of the NaZni ₃ -type phase and 9% by weight of α-Fe. Depending on the press conditions, the density of the pressed material is 70 to 90% of the theoretical density of the material which consists of 91% by weight of LaFen, ₆ Sii, ₄ and 9% by weight of α-Fe.

For the investigation of the magnetic properties, 2 plates are cut from a cylindrical hot-pressed material having dimensions of 8 mm × 4 mm × 1 mm.

The hot-pressed material with the composition LaFen, 6Sii, ₄ shows a maximum entropy change ΔS _ma χ of 110 kJ / m ³ K at 194 K with a magnetic field change of 2 Tesla. The half-width is 10.5 K and the relative cooling capacity is 1, 3 MJ / m ³ . The entropy change and the relative cooling power remain unchanged after thermal cycling.

The adiabatic temperature change ΔT _aC ι remains unchanged after the thermal and magnetic field alternating stress and is 4.3 K during cooling from room temperature and when heating 170 K to room temperature with a magnetic field change of 1.9 Tesla. The thermal hysteresis is less than 1 K, ie significantly lower compared to the solid material. The magnetic field dependence of the adiabatic temperature change is nearly hysteresis-free (less than 0.05 T).

The mechanical integrity of the hot-pressed material remains after multiple thermal or field cycling cycles.

Example 2

From the elements La, Fe and Si, an alloy having the composition LaFen _{, 6} Sii _{, 4 is} produced by means of an arc melting process. The alloy is then rapidly solidified at the surface speed of the copper wheel of 30 m / s and then heat-treated at 1050 ^° C. for 2 hours [J. Lyubina et al., J. Magn. Magn. Mater. 320, 2252 (2008)]. The resulting material is in the form of a band with a thickness of 60 microns and consists of 90 wt .-% of the NaZni ₃ - type phase and 10 wt .-% of α-Fe.

From the pulverized rapidly solidified strips, a porous, foam-like material is produced by pressing at room temperature (cold pressing) and pressing pressure of 500 MPa. The dimensions of the pressed LaFen _{, 6} Sii _{, 4} alloy are 11 mm diameter x 1 mm height and the density is 85% of the theoretical density of the material.

The cold-pressed LaFen, 6Sii, ₄ alloy shows a maximum magnetic entropy change ΔS _ma χ of 145 kJ / m ³ K at 193 K and a magnetic field change of 2 Tesla. The half width is 8.3 K and the relative cooling capacity is 1.5 MJ / m ³ . The adiabatic temperature change ΔT _aC ι remains unchanged after the thermal and magnetic field alternating stress and is 4.3 K at 193 K when cooling from room temperature and when heating 170 K to room temperature with a magnetic field change of 1.9 Tesla. It is the thermal hysteresis less than 0.5 K. The magnetic field dependence of the adiabatic temperature change is almost hysteresis-free.

This cold-pressed LaFen _{, 6} Sii _{, 4} -l_egierung is hydrogenated at 400 ⁰ C in 0.5 MPa hydrogen gas. The hydrogen concentration of z = 1.64 was measured by hot extraction. This corresponds to a composition of LaFen, 6Sii, ₄ Hi ₆₄ -

After the hydrogen loading of the cold-pressed material, the temperature at which the maximum of the entropy change or the adiabatic temperature change occurs, shifts to 338 K. The adiabatic temperature change ΔT _aC ι remains unchanged after the thermal and magnetic field alternating stress and is 3.7 K during cooling from room temperature and when heating 170 K to room temperature with a magnetic field change of 1.9 Tesla. The temperature and magnetic field dependence of the adiabatic temperature change are almost hysteresis-free.

Alternatively, the rapidly solidified and heat-treated ribbons are hydrogenated at 400 ^° C. in 0.5 MPa hydrogen gas and then produced at a temperature of 650 K and a compression pressure of 500 MPa. The adiabatic temperature change ΔT _aC ι remains unchanged after the thermal and magnetic field alternating stress and is 3.6 K at 335 K with a magnetic field change of 1.9 Tesla. The temperature and magnetic field dependence of the adiabatic temperature change are almost hysteresis-free.

The pressing at a temperature of 650 K under vacuum can be used at the same time for setting the Curie temperature or application temperature. When pressing in a vacuum of 1 Pa at 423 K, the temperature at which the maximum of the entropy change or adiabatic temperature change occurs shifts to 300 K.

The mechanical integrity of the hot or cold pressed material or material pressed at a temperature of 650 is maintained after multiple thermal or field cycling cycles.

Claims

claims

A magnetic alloy material which exhibits a magnetocaloric effect and which has a foam-like structure with an open porosity of 1% to 50% and / or a closed porosity of at least 1%, or wherein the particles of the magnetic alloy material in a matrix material with a higher ductility than the magnetic alloy material are embedded.

The alloy material according to claim 1, wherein> 35% by volume of the magnetic alloy material has a NaZni ₃ type crystal structure.

The alloy material according to claim 2, wherein at least 50% by volume of the magnetic alloy material has a NaZni ₃ type crystal structure.

The alloy material according to claim 3, wherein 80-90 vol% of the magnetic alloy material has a NaZni ₃ type crystal structure.

5. The alloy material according to claim 1, wherein the magnetic alloy material has a composition according to the formula:

RaFe- | 00-axy-zTχMyL _z with

R = La or a combination of La with Ce, Pr, Nd, Sm, Gd, Tb,

Dy, Ho, Er, Tm, Yb, Lu and / or Y,

T = at least one element selected from the group Sc, Ti, V, Cr,

Mn, Co, Ni, Cu and / or Zn,

M = Al, Si, P, Ga, Ge, In and / or Sn,

L = H, B, C and / or N,

5 <_a <11 and 0 <x <12 and 2 <y <20 and 0 <z <18, (everything in atomic

The alloy material according to claim 5, wherein the conditions 2 <z <for changing the Curie temperature of the magnetic alloy material 15 atom% and / or 3 <_y <16 and / or 0.3 <x <9 are realized, wherein with varying proportion z and / or y and / or x, the Curie temperature changes between 170 K and 400 K.

The alloy material according to claim 1, wherein the foam-like structure of the magnetic alloy material has an open porosity of 2 to 50% and / or a closed porosity of 2 to 50%.

The alloy material according to claim 1, wherein particles of the magnetic alloy material having a particle size of 10 nm to 1 mm are embedded in a matrix material.

9. The alloy material according to claim 1, wherein the matrix material having a higher ductility than the magnetic alloy material comprises at least one of Al, Ag, Au, Bi, C, Co, Cu, Fe, Ga, Ni, Pb, Pd, Pt, Sn, Ti, Zn or combinations and / or reaction products thereof.

10. The alloy material according to claim 1, wherein in addition to the matrix material, a second material of at least one element of Al, Ag, Au, Bi, C, Co, Cu, Fe, Ga, Ni, Nb, Pb, Pd, Pt, Sn, Ta, Ti, V, Zn, Zr or combinations and / or reaction products also with the matrix material thereof is present.

The alloy material of claim 1, wherein the matrix material has at least 10% higher ductility than the magnetic alloy material.

12. An alloy material according to claim 1, wherein the particles of the magnetic alloy material in the form of a band, a wire, a plate, a foil or a flake, a needle or in the form of powder particles.

13. A process for producing a magnetic alloy material according to any one of claims 1 to 12, wherein the magnetic alloy material to a foam-like structure by means of foaming or Compaction processed or mixed particles of the magnetic alloy material with a matrix material, which has a higher ductility than the magnetic alloy material, and then heated to the extent that the matrix material forms the matrix around the particles of the magnetic alloy material.

14. The method of claim 13, wherein the compaction is performed by hot or cold pressing.

15. The method of claim 13, wherein the foaming is carried out by applying a suspension with particles of the magnetic alloy material to a foam-like structure and dried, and then the foam-like structure is burned out or pyrolyzed.

16. The method of claim 13, wherein particles of the magnetic alloy material and the matrix material are mixed and processed into a shaped body and subsequently heated this shaped body to a temperature at which the matrix material at least softens and covers the particles of the magnetic alloy material substantially completely.

17. The method of claim 13, wherein the application temperature is adjusted by applying a vacuum.